1. Field of the Invention
The present invention relates to a printed circuit board capable of improving an integration degree in mounting components and wiring by virtue of a core layer and built-up layers, and more particularly, to a multi-layer printed circuit board in which via-holes and conductive layers are formed on the core layer and on the built-up layers and the conductive layers are electrically connected, thereby improving an integration degree in mounting components and wiring of the printed circuit board as well as shortening the length of wiring.
2. Description of the Background Art
FIG. 1 is a sectional view showing a construction of a multi-layer printed circuit board in accordance with one conventional art.
As shown in the drawing, the multi-layer printed circuit board includes a copper thin film layer 11 formed between each insulation layer (insulating resin layer) 10, a through hole 12 formed to penetrate a predetermined portion of the copper thin film layer 11 and the insulation layer 10, and conductive layers 12-1 and 12-2 formed on the inner wall and the uppermost surface of the through hole 12 by electrodeless plating or electroplating. The through hole 12 is filled with an insulating resin.
The conductive layers 12-1 and 12-2 of the multi-layer printed circuit board are electrically connected with the copper thin film layer 11 formed between the insulation layers 10.
However, the problem is that the conductive layers, 12-1 and 12-2, which are connected with the copper thin film layers 11 formed between the insulation layers 10, are also connected with the copper thin film layer 11 that is not required to be connected.
In addition, the through hole 12 is normally formed by using a drill that is adjusted by a computer numerical control method. Currently, it is possible to form a hole having a diameter of 250 xcexcm, but the integration in mounting components for a high concentration and high integrity is reduced.
Also, a land (not shown) having a diameter of 100 xcexcm necessarily exists in the vicinity of the hole for connection with other mounted components, which inevitably leads to a reduction in mounting components and wiring.
Moreover, since the wiring in the circuit pattern formed on the uppermost and the lowermost surfaces is formed by detouring the circumference of the hole 12, the wiring of the circuit pattern is lengthened, and thus, a signal transmission is delayed and a noise occurs.
FIG. 2 is a sectional view showing a construction of a multi-layer printed circuit board in accordance with another conventional art.
As shown in the drawing, the multi-layer printed circuit board includes a first substrate 20A, a core substrate 20B and a second substrate 20C.
The first substrate 20A and the second substrate 20C have the same construction, thus, descriptions are made only for the first substrate 20A.
The first substrate 20A includes a copper thin film layer 22 formed between insulation layers (insulating resin layers) 23, a hole 27 formed to penetrate a predetermined portion of the copper thin film layer 22 and the insulation layer 23, and first conductive layers 24 and 26 formed on the inner wall and on the surface of the hole 27 by the electrodeless plating or electroplating.
The core substrate 20B is constructed by forming the copper thin film layers 20 on the upper and lower surface of the insulation layer 21. The core substrate 20B is attached between the first substrate 20A and the second substrate 20C. That is, after a resin 30 is, inserted between the first substrate 20A and the core substrate 20B and between the core substrate 20B and the second substrate 20C, when the substrates 20A, 20B and 20C are pressed by applying heat, the resin 30 is melted, filling the hole 27. And then as the resin 30 is hardened, the first substrate 20A and the second substrate 20C and the core substrate 20B are attached to each other.
Thereafter, the through hole 28 is formed penetrating predetermined portions of the substrates 20A, 20B and 20C, and second conductive layers 25 and 29 are formed on the inner wall and on the surface of the through hole 28 by the electrodeless plating or the electroplating. And then, a predetermined circuit pattern is formed on the uppermost and the lowermost surface of the substrate by a typical etching process.
In this conventional art, the second conductive layers 25 and 29 formed in the multi-layer printed circuit board are electrically connected with the copper thin film layers 20 and 22 formed between the insulation layers 23 and 30.
However, since there exists the through hole 28 on the first substrate 20A, the second substrate 20C and the core substrate 20B, the integration degree in mounting components and wiring are reduced.
In addition, since the wiring in the circuit pattern formed on the uppermost and the lowermost surfaces is formed by detouring the circumference of the hole 12, the wiring of the circuit pattern is lengthened, and thus, a signal transmission is delayed and a noise occurs.
Moreover, as the second conductive layer 25 is formed on the first conductive layer 24, the conductive layers formed on the upper and lower surface of the multilayer printed circuit board become thick. Thus, it is difficult to form a fine circuit pattern and its processes are complicated, resulting in a low productivity.
Therefore, an object of the present invention is to provide a multi-layer printed circuit board in which via-holes and conductive layers are formed on the core layer and on the built-up layers and the conducive layers are electrically connected, thereby improving the integration degree in mounting components and wiring of the printed circuit board as well as shortening the length of wiring.
To achieve these and other advantages and in accordance with the purposed of the present invention, as embodied and broadly described herein, there is provided a multi-layer printed circuit board including a core layer having a first circuit pattern formed on the upper surface of a first insulation layer and a first conductive layer formed on the lower surface of the first insulation layer; and built-up layers formed on the upper and lower surface of the core layer and having a second circuit pattern electrically connected with the first circuit pattern.
To achieve the above object, there is also provided a method for fabricating a multi-layer printed circuit board including the steps of: forming a core layer in a manner that a first circuit pattern is formed on the upper surface of the first insulation layer and a first conductive thin film and a first conductive layer are formed on the lower surface of the first insulation layer; and forming built-up layers in a manner that a second insulation layer on the upper and lower surface of the core layer and a second circuit pattern is formed on the surface of the second insulation layer.